The present invention relates to a method for manufacturing a hydrogen-silsesquioxane resin by the hydrolytic condensation of trichlorosilane (HSiCl3). This invention also relates to a method for manufacturing a hydrogen-silsesquioxane resin which allows more or less complete re-utilization of the solvent, sulfuric acid and surfactants used, without any loss of these compounds.
Hydrogen-silsesquioxane resins are useful precursor substances for silica-containing ceramic coatings. For example, U.S. Pat. No. 4,756,977 discloses a method for forming a coating in which a hydrogen-silsesquioxane resin is diluted with a solvent, applied to a substrate, and then forming a ceramic or ceramic-like coating by heating.
When trichlorosilane is subjected to hydrolytic condensation caused by direct contact with water, the reaction occurs abruptly, and the resin that is produced gels. Accordingly, various methods for manufacturing hydrogen-silsesquioxane resins (which are hydrolytic condensation products of trichlorosilane) while preventing such gelation have been proposed in the past.
For example, a method in which a hydrogen-silsesquioxane resin is manufactured by subjecting a solution of trichlorosilane dissolved in a hydrocarbon solvent to hydrolytic condensation while mixing said solution in a two-phase reaction medium consisting of concentrated sulfuric acid and an aromatic hydrocarbon is disclosed in Japanese Patent Application Kokoku No. Sho 47-31838. In that patent application, the aforementioned concentrated sulfuric acid and aromatic hydrocarbon react to produce an arylsulfonic acid hydrate, and the water of hydration in this hydrate contributes to the hydrolytic condensation of the aforementioned trichlorosilane. Then, a hydrogen-silsesquioxane resin produced by this hydrolytic condensation is obtained from the organic phase, and a mixture of concentrated sulfuric acid, arylsulfonic acid hydrate and non-hydrated arylsulfonic acid are obtained from the concentrated sulfuric acid phase. The non-hydrated arylsulfonic acid is obtained in large quantities. In experiments performed by the present inventors, it was found that when water is added to the concentrated sulfuric acid phase in an attempt to recover and reuse the arylsulfonic acid contained in said phase, precipitation occurs (for unknown reasons), so that the arylsulfonic acid cannot be reused. For this reason, large quantities of organic solvent and sulfuric acid are lost.
A method in which a hydrogen-silsesquioxane resin is formed by adding a solution containing trichlorosilane to a hydrolysis medium containing an arylsulfonic acid hydrate while this hydrolysis medium is agitated in described in Japanese Patent Application Kokai No. Hei 6-41518. That patent application describes a method in which concentrated sulfuric acid is added to toluene or benzene as a method for manufacturing the above mentioned hydrolysis medium containing an arylsulfonic acid hydrate. Furthermore, it is indicated that the water of hydration contained in the arylsulfonic acid hydrate thus formed is utilized in the hydrolytic condensation of the trichlorosilane. No mention is made concerning the re-utilization of the non-hydrated arylsulfonic acid that is produced, or concerning the recovery in any way of the organic solvent or sulfuric acid in that reference.
The present invention relates to a method for manufacturing a hydrogen-silsesquioxane resin by the hydrolytic condensation of trichlorosilane (HSiCl3). An object of the present invention is to provide a method for manufacturing a hydrogen-silsesquioxane resin which allows more or less complete re-utilization of the solvent, sulfuric acid and surfactants used, essentially without loss of these compounds.
The present invention pertains to a method for the manufacture of a hydrogen-silsesquioxane resin by the hydrolytic condensation of trichlorosilane (HSiCl3) in a two-phase system consisting of (I) aqueous phase: an aqueous solution in which sulfuric acid and an organic sulfonic acid selected from aromatic sulfonic acids or aliphatic sulfonic acids are dissolved, with the sulfuric acid comprising 80 to 96 wt % of the total amount of sulfuric acid and water present in the aqueous phase (in cases where the organic sulfonic acid is a hydrate, this includes the water of hydration contained in said hydrate); and
(II) organic phase: a solution formed by dissolving the organic sulfonic acid at the rate of 0.008 moles/liter or greater in a halogenated hydrocarbon solvent which is capable of dissolving the trichlorosilane, and which has no substantial reactivity with respect to sulfuric acid.
The present invention is a method for manufacturing a hydrogen-silsesquioxane resin in which trichlorosilane (HSiCl3) is subjected to a hydrolytic condensation in a two-phase system consisting of an aqueous phase (I) and an organic phase (II) shown below:
(I) aqueous phase: an aqueous solution in which sulfuric acid and an organic sulfonic acid selected from aromatic sulfonic acids or aliphatic sulfonic acids are dissolved, with the sulfuric acid comprising 80 to 96 wt % of the total amount of sulfuric acid and water present in the aqueous phase (in cases where the organic sulfonic acid is a hydrate, this includes the water of hydration contained in said hydrate); and
(II) organic phase: a solution formed by dissolving the organic sulfonic acid at the rate of 0.008 moles/liter or greater in a halogenated hydrocarbon solvent which is capable of dissolving the trichlorosilane, and which has no substantial reactivity with respect to sulfuric acid; here, the weight ratio of the organic sulfonic acid (excluding the weight of the water of hydration contained in the compound in cases where said organic sulfonic acid is a hydrate) relative to the total weight of the sulfuric acid, organic sulfonic acid and (if necessary) water that are added in order to form the two phases is 5 wt % or greater.
As described above, the aqueous phase in the present invention comprises water, a large quantity of sulfuric acid and an organic sulfonic acid comprising the major portion of the aqueous phase. It is necessary that the concentration of sulfuric acid in this aqueous phase be in the range of 80 wt % to 96 wt % of the combined weight of water and sulfuric acid present in the aqueous phase. Described herein, the term xe2x80x9cwater present in the aqueous phasexe2x80x9d naturally also includes water contained in the aqueous solution of sulfuric acid that is added to the aqueous phase, and water separated from organic sulfonic acids having water of hydration in the aqueous phase.
In cases where the concentration of sulfuric acid is outside the above mentioned range, the yield drops noticeably even if the other conditions of the present invention are satisfied.
Furthermore, the sulfuric acid that is used to form the aqueous phase may be an aqueous solution of sulfuric acid, 100% sulfuric acid or fuming sulfuric acid. The sulfuric acid used for the purpose of forming the aqueous phase is ordinarily added in the form of an aqueous solution of sulfuric acid. In cases where the amount of water that may be contained in the sulfuric acid and the amount of water of hydration that may be possessed by the organic sulfonic acid are insufficient for the hydrolytic condensation of the trichlorosilane, water must be separately added.
A solvent which can dissolve both trichlorosilane and a surfactant, and which has no substantial reactivity with respect to sulfuric acid, is selected as the halogenated hydrocarbon solvent used in the organic phase in the present invention. Here, the term xe2x80x9cno substantial reactivityxe2x80x9d means that no reaction occurs when the halogenated hydrocarbon solvent and the sulfuric acid are used in the manufacturing method of the present invention, or that the reaction rate is extremely slow so that the solvent is consumed by the reaction at a level that causes no practical problems.
Examples of such halogenated hydrocarbon solvents include aliphatic halogenated hydrocarbon solvent, especially aliphatic halogenated hydrocarbon solvents with 3 to 12 carbon atoms, and aromatic halogenated hydrocarbon solvents, especially aromatic halogenated hydrocarbon solvents with 6 to 18 carbon atoms. The following compounds may be cited as examples (although the present invention is not limited to these examples): isopropyl chloride, 1-chloropropane, 1-chlorobutane, 1-chloropentane, 1-chlorooctane, trichloroethylene, perchloroethylene, bromobenzene, chlorobenzene, o-dichlorobenzene and p-trifluoromethylchlorobenzene.
Examples of preferred solvents from the standpoints of yield and non-reactivity with sulfuric acid, etc. include isopropyl chloride, 1-chloropentane, chlorobenzene, o-dichlorobenzene and p-trifluoromethylchlorobenzene (para-CF3xe2x80x94C6H4xe2x80x94Cl).
The organic sulfonic acids used in the present invention are selected from aromatic sulfonic acids or aliphatic sulfonic acids which are soluble in both water and the halogenated hydrocarbon solvent used in the manufacturing method of the present invention. Since aromatic sulfonic acids and aliphatic sulfonic acids have a low reactivity with the sulfuric acid used in the manufacturing method of the present invention, these compounds are capable of exhibiting a stable surfactant function in the reaction system.
The aromatic sulfonic acids have structures in which xe2x80x94SO3H groups are bonded directly to aromatic rings. Organic substituent groups may be bonded to these aromatic rings, or may be absent. There are no particular restrictions on these compounds, as long as the compounds are soluble in both water and halogenated hydrocarbon solvents. These sulfonic acids may be unsubstituted aromatic sulfonic acids or substituted aromatic sulfonic acids. Furthermore, these compounds are not restricted in terms of the presence or absence of water of hydration. Examples of these acids include the following:
(1) Unsubstituted Aromatic Sulfonic Acids such as benzenesulfonic acid (C6H5SO3H.1.5xcx9c2.0H2O). This compound may also be an acid anhydride.
(2) Substituted Aromatic Sulfonic Acids such as
(a) alkylbenzenesulfonic Acids
{circle around (1)} Toluenesulfonic acid (CH3C6H4SO3H); this may be o-toluenesulfonic acid, p-toluenesulfonic acid or m-toluene sulfonic acid, and may have water of hydration.
{circle around (2)} 2,5-Dimethylbenzenesulfonic acid
{circle around (3)} 3,4-Dimethylbenzenesulfonic acid
{circle around (4)} m-Xylenesulfonic acid
(b) Aromatic sulfonic acids substituted by unsaturated groups, such as styrenesulfonic acid, etc., may be cited as examples of substituted aromatic sulfonic acids other than those listed under (a).
(3) Halogenated Benzenesulfonic Acids
4-Chlorobenzenesulfonic acid (Clxe2x80x94C6H4xe2x80x94SO3H)
4-Chlorobenzenesulfonic acid monohydrate (Clxe2x80x94C6H4xe2x80x94SO3H.H2O)
The above aliphatic sulfonic acids have structures in which xe2x80x94SO3H groups are bonded to aliphatic groups. There are no particular restrictions on these compounds, as long as the compounds are soluble in both water and halogenated hydrocarbon solvents, including saturated aliphatic sulfonic acids and unsaturated aliphatic sulfonic acids. For example, such acids may include:
(1) Saturated Aliphatic Sulfonic Acids
Methanesulfonic acid (CH3xe2x80x94SO3H)
Ethanesulfonic acid (C2H5xe2x80x94SO3H)
(2) Unsaturated Aliphatic Sulfonic Acids
Alkenylsulfonic acids with 3 or 4 carbon atoms
If the degree of non-reactivity with respect to sulfuric acid is taken into consideration, the following organic sulfonic acids are preferred: benzenesulfonic acid, hydrates of benzenesulfonic acid, p-toluenesulfonic acid, hydrates of p-toluenesulfonic acid, and ethanesulfonic acid.
In the present invention, two phases comprising an organic phase and an aqueous phase comprising the reaction medium are formed. Sulfuric acid, an organic sulfonic acid, a halogenated hydrocarbon and (if necessary) water are added in order to form these two phases. Among these compounds, it is desirable that the weight ratio of the organic sulfonic acid relative to the combined weight of the sulfuric acid and water that is added if necessary (in cases where water of hydration is present, the weight of this water is excluded) be 5 wt % or greater. In cases where the ratio is less than this value, the yield of the hydrogen-silsesquioxane resin drops noticeably even if the other conditions of the present invention are satisfied. There are no particular restrictions on the upper limit of the ratio, as long as the ratio is in a range that allows dissolution of the organic sulfonic acid used in the aqueous phase; ordinarily, however, an amount in the range of 5 wt % to 40 wt % is used. In the case of organic sulfonic acids which have a high solubility in the aqueous phase, there may be cases in which a sufficient yield can be obtained even if the upper limit of the above range is exceeded; however, considering the economy of the yield of the hydrogen-silsesquioxane resin and the amount of organic sulfonic acid used, the above range is recommended.
In the present invention, a two-phase system comprising the aqueous phase and organic phase is prepared beforehand, and trichlorosilane is added to this two-phase system. It is preferable to add a trichlorosilane solution prepared by dissolving trichlorosilane in a halogenated hydrocarbon solvent. In the two-phase system comprising an aqueous phase and organic phase to which the trichlorosilane solution is added, it is preferred that the organic sulfonic acid be present at the rate of 0.008 moles/L or greater in the organic phase. If the organic sulfonic acid concentration is less than this, the yield of the hydrogen-silsesquioxane resin drops noticeably even if the other conditions of the present invention are satisfied. There is no particular stipulation of the upper limit of this concentration; ordinarily, however, a concentration of up to 2 moles/L is used. A yield that is sufficient in practical terms is insured if an organic sulfonic acid is present in an amount up to this level in the organic phase.
Typically, the method of manufacture of the present invention is as follows:
1) An organic sulfonic acid solution is prepared by dissolving the organic sulfonic acid in an aqueous solution of sulfuric acid (hereafter referred to as a xe2x80x9corganic sulfonic acid solutionxe2x80x9d). This solution may be prepared by adding the necessary amount of water.
2) The organic sulfonic acid solution is dissolved in the halogenated hydrocarbon solvent, thus preparing a reaction medium consisting of two phases, i.e., an aqueous phase and an organic phase.
3) A trichlorosilane solution is prepared by dissolving HSiCl3 in the halogenated hydrocarbon solvent.
4) While the reaction medium is vigorously agitated, the trichlorosilane solution is gradually added. Dropwise addition may be cited as a common method used to accomplish this addition operation. The time required for the addition of the trichlorosilane solution depends on the amount of trichlorosilane solution added; however, in cases where the trichlorosilane solution consists of trichlorosilane and a halogenated hydrocarbon solvent at a weight ratio of approximately 1:1, a time of several minutes to several tens of minutes is sufficient.
5) Following the completion of the above addition, the system is agitated for (e.g.) approximately 30 minutes to 120 minutes, ordinarily at a temperature ranging from 10xc2x0 C. to a temperature below the boiling point of trichlorosilane. In practical terms, a temperature ranging from room temperature to approximately 25xc2x0 C. is selected.
6) Next, the organic phase and aqueous phase are separated using a separating funnel.
7) The organic phase is washed by ordinary methods. For example, the organic phase may be neutralized by the addition of calcium carbonate, and then dehydrated by the addition of magnesium sulfate, after which the organic phase is filtered.
8) The solid matter that is obtained is stripped, thus producing a hydrogen-silsesquioxane resin.
In order to achieve the hydrolytic condensation of 1 mole of HSiCl3, it is necessary to use 1.5 moles of water or more. In the present invention, it is preferred to use such an amount of water or more. Ordinarily, the water content added is adjusted in accordance with the amount of HSiCl3 used. Furthermore, in cases where the necessary amount of water is insured by water originating in the aqueous solution of sulfuric acid or in the organic sulfonic acid (hydrate), it is of course not necessary to add water separately.
Embodiments of the present invention will be described below. A first embodiment is a method for making a hydrogen-silsesquioxane resin wherein trichlorosilane (HSiCl3) is subjected to a hydrolytic condensation reaction which comprises preparing an aqueous phase by dissolving an organic sulfonic acid selected from aromatic sulfonic acids or aliphatic sulfonic acids in aqueous sulfuric acid, wherein the sulfuric acid comprises 80 to 96 wt % of the total amount of sulfuric acid and water present in the aqueous phase. Then a reaction medium is prepared wherein the reaction medium comprises an aqueous phase and an organic phase by adding the aqueous phase to a halogenated hydrocarbon solvent which is capable of dissolving the trichlorosilane, and which has no substantial reactivity with respect to sulfuric acid. Next trichlorosilane (HSiCl3) is added to the reaction medium while mixing the reaction medium. The organic phase containing the hydrogen-silsesquioxane and aqueous phase are separated and the hydrogen-silsesquioxane resin is removed from the organic phase.
In a second embodiment, the hydrolytic condensation is performed by adding a solution prepared by dissolving trichlorosilane in the halogenated hydrocarbon solvent to prior to adding to the two-phase system.